From b98f7a5cbb3f49f8104a641b17a9be87b6b851fc Mon Sep 17 00:00:00 2001
From: John Darrington <address@hidden>
Date: Wed, 14 Jan 2015 10:08:10 +0100
Subject: [PATCH] Remove decimal_multiply. Fix overflow handling in
 decimal_int_multiply and add tests.

---
 src/math/decimal.c        |   18 +++++++-------
 src/math/decimal.h        |    1 -
 tests/math/decimal-test.c |   57 +++++++++++++++++++++++++++++++++++++--------
 3 files changed, 56 insertions(+), 20 deletions(-)

diff --git a/src/math/decimal.c b/src/math/decimal.c
index ba33e76..0655834 100644
--- a/src/math/decimal.c
+++ b/src/math/decimal.c
@@ -299,23 +299,23 @@ decimal_cmp (const struct decimal *d1, const struct decimal *d2)
 }
 
 
-/* Multiply DEST by SRC */
-void
-decimal_multiply (struct decimal *dest, const struct decimal *src)
-{
-  dest->ordinate *= src->ordinate;
-  dest->mantissa += src->mantissa;
-}
-
-
 /* Multiply DEST by M */
 void
 decimal_int_multiply (struct decimal *dest, ord_t m)
 {
+  if (m != 0)
+    while (llabs (dest->ordinate) > llabs (ORD_MAX / m))
+      {
+        dest->ordinate /= 10;
+        dest->mantissa++;
+      }
+
   dest->ordinate *= m;
+
   reduce (dest);
 }
 
+
 /* Divide DEST by M */
 void
 decimal_int_divide (struct decimal *dest, ord_t m)
diff --git a/src/math/decimal.h b/src/math/decimal.h
index 2a3fd60..b5740f6 100644
--- a/src/math/decimal.h
+++ b/src/math/decimal.h
@@ -93,7 +93,6 @@ void normalise (struct decimal *d1, struct decimal *d2);
 void decimal_init (struct decimal *dec, ord_t ord, mant_t mant);
 void decimal_init_from_string (struct decimal *dec, const char *s);
 int decimal_cmp (const struct decimal *d1, const struct decimal *d2);
-void decimal_multiply (struct decimal *dest, const struct decimal *src);
 void decimal_int_multiply (struct decimal *dest, ord_t m);
 void decimal_int_divide (struct decimal *dest, ord_t m);
 void decimal_divide (struct decimal *dest, const struct decimal *src);
diff --git a/tests/math/decimal-test.c b/tests/math/decimal-test.c
index aa4d244..3e1e64e 100644
--- a/tests/math/decimal-test.c
+++ b/tests/math/decimal-test.c
@@ -200,21 +200,26 @@ test_addition (const struct decimal *one_, const struct decimal *two)
   assert (strcmp (sdsum1, sdsum2) == 0);
 }
 
+
 void
-test_multiplication (const struct decimal *one_, const struct decimal *two)
+test_multiplication (const struct decimal *d, int m)
 {
-  struct decimal one = *one_;
-  double d1 = decimal_to_double (&one);
-  double d2 = decimal_to_double (two);
-  
-  decimal_multiply (&one, two);
-  
-  double dprod = decimal_to_double (&one);
-  
-  assert (dprod == d1 * d2);
+  char b1[256];
+  char b2[256];
+  struct decimal dest = *d;
+  double x = decimal_to_double (&dest);
+
+  decimal_int_multiply (&dest, m);
+
+  double y = decimal_to_double (&dest);
+
+  snprintf (b1, 256, "%g", m * x);
+  snprintf (b2, 256, "%g", y);
+  assert (0 == strcmp (b1, b2));
 }
 
 
+
 int 
 main (int argc, char **argv)
 {
@@ -306,5 +311,37 @@ main (int argc, char **argv)
   }
 
 
+  {
+    struct decimal m = {10, 0};
+
+    test_multiplication (&m, 11);
+  }
+
+
+  {
+    struct decimal m = {ORD_MAX - 2, 0};
+
+    test_multiplication (&m, 11);
+  }
+
+
+  {
+    struct decimal m = {34, 0};
+
+    test_multiplication (&m, 0);
+  }
+
+  {
+    struct decimal m = {34, -20};
+
+    test_multiplication (&m, 33);
+  }
+
+  {
+    struct decimal m = {304, 2};
+
+    test_multiplication (&m, -33);
+  }
+
   return 0;
 }
-- 
1.7.10.4